Thought this article was fascinating.
We’re accustomed to thinking of our cells sharing an identical set of genes, faithfully copied ever since we were mere fertilized eggs. When we talk about
our genome — all the DNA in our cells — we speak in the singular. But over the course of decades, it has become clear that the genome doesn’t just vary from person to person. It also varies from cell to cell. The condition is not uncommon: We are all mosaics.
For some people, that can mean developing a serious disorder like a heart condition. But mosaicism also means that even healthy people are more different from one another than scientists had imagined.
In one study, they plucked neurons from the brain of a 17-year-old boy who had died in a car accident. They sequenced the DNA in each neuron and compared it to the DNA in cells from the boy’s liver, heart and lungs. Every neuron, the researchers found, had hundreds of mutations not found in the other organs. But many of the mutations were shared only by some of the other neurons.
It occurred to Dr. Walsh that he could use the mutations to reconstruct the cell lineages — to learn how they had originated. The researchers used the patterns to draw a sort of genealogy, linking each neuron first to its close cousins and then its more distant relatives. When they had finished, the scientists found that the cells belonged to five main lineages. The cells in each lineage all inherited the same distinctive mosaic signature. Even stranger, the scientists found cells in the boy’s heart with the same signature of mutations found in some brain neurons. Other lineages included cells from other organs.
Based on these results, the researchers pieced together a biography of the boy’s brain. When he was just an embryonic ball in the womb, five lineages of cells had emerged, each with a distinct set of mutations. Cells from those lineages migrated in different directions, eventually helping to produce different organs — including the brain.
/www.nytimes.com/2018/05/21/science/mosaicism-dna-genome-cancer.html